1. Field of the Invention
The present invention relates to a fixing apparatus and to an image forming apparatus including the same. More particularly, the invention relates to a fixing apparatus having an electromagnetic valve attaching portion, and to an imaging apparatus including such a fixing apparatus.
2. Description of the Related Art
Hitherto, an image forming apparatus including a fixing apparatus provided with an electromagnetic valve attaching portion has been known (see, for examples, JP-UM-A-56-89215 and JP-UM-A-58-105106).
The JP-UM-A-56-89215 discloses a structure of a first example of the conventional apparatus, in which a catching portion is provided on an outer surface of a flange of a solenoid (a electromagnetic valve), and a caught portion is provided in a yoke (an electromagnetic valve mounting portion) by being cut upwardly from a chassis (a frame). In this structure disclosed in the JP-UM-A-56-89215, the solenoid (the electromagnetic valve) and the yoke (the electromagnetic valve mounting portion) are fixed by engaging the catching portion provided on the flange of the solenoid (the electromagnetic valve) with the caught portion of yoke (the electromagnetic valve mounting portion).
Further, the JP-UM-A-58-105106 discloses a structure of a second example of the conventional apparatus, in which the solenoid (the electromagnetic valve) is fixed by using metal fittings, each of which are provided with claw elements, and a frame element provided with a groove that engages with the claw elements of the metal fittings. Concretely, according to the JP-UM-A-58-105106, the solenoid (the electromagnetic valve) is fixed by fitting the claw elements of the metal fittings into the groove of the frame element.
FIG. 15 is a perspective view illustrating the entire configuration of a laser printer including a conventional fixing apparatus provided with a pressure releasing mechanism. FIG. 16 is a side view, which is taken in the direction of an arrow B and illustrates the conventional fixing apparatus of the laser printer shown in FIG. 15. FIG. 17 is a top view illustrating a pressure releasing mechanism of the conventional fixing apparatus shown in FIG. 16. FIG. 18 is a view illustrating a state in which an electromagnetic valve of the pressure releasing mechanism of the conventional fixing apparatus shown in FIG. 17 is energized. FIG. 19 is a perspective view illustrating an exploded condition of the electromagnetic valve of the pressure releasing mechanism of the conventional fixing apparatus. FIG. 20 is a perspective view illustrating amounted condition of a cam and the electromagnetic valve in the pressure releasing mechanism of the conventional fixing apparatus. Incidentally, the conventional fixing apparatuses each having the pressure releasing mechanism are disclosed in, for example, JP-A-54-48255 and JP-A-2-266385. First, the configuration of a conventional laser printer 200 is described by referring to FIG. 15. In the laser printer 100 including a conventional fixing apparatus that has an electromagnetic valve mounting portion, as shown in FIG. 15, a toner cartridge 102 for transferring an image on recording paper 101 by using toner is detachably mounted. A fixing apparatus 103 for fixing a toner image formed with toner, which is transferred by the toner cartridge 102, on the recording paper 101 is provided at the rear side of the toner cartridge 102. This fixing apparatus 103 is supported by a frame 104. Further, a gear 105 for rotating a fixing roller 106, (see FIG. 16) provided in the fixing apparatus 103 is provided on a side portion of the fixing apparatus 103.
Next, the entire configuration of the conventional fixing apparatus having the electromagnetic mounting portion is described hereinbelow by referring to FIG. 16. As shown in FIG. 16, an entrance guide 107 for guiding the recording paper 101 toward the fixing roller 106 is provided at the entrance side of the fixing apparatus 103. The fixing roller 106 for fixing a toner image, which is transferred to the recording paper 101, by heating the recording paper 101 is provided in a sheet feeding direction of an entrance guide 107. This fixing roller 106 is constituted by a metallic tube having a built-in heater (not shown) for heating the paper. Further, two bearings for rotatably supporting the fixing roller 106 are attached to both sides of the fixing roller 106, respectively.
Furthermore, a pressure roller 109 for pressing the recording paper 101 against the fixing roller 106 is provided under the fixing roller 106 in such a way as to be brought into contact with the fixing roller 106 by a predetermined pressing force. A bearing 111 for rotatably supporting the pressure roller 109 is attached to an end portion of a shaft 110 of this pressure roller 109. This bearing 111 is held by a bearing holding member 113 fitted into a concave portion 112a of a crank-plate 112.
Further, this crank-plate 112 is rotatably mounted on a shaft 114 serving as a supporting point. An extension coil spring 115 is attached to a spring attaching portion 112b of the crank-plate 112. This extension coil spring 115 is pressed in such a way as to turn the crank-plate 112 in a direction in which the pressure roller 109 pushes the fixing roller 106.
Furthermore, a separating claw 116 is placed in the sheet feeding direction of the fixing roller 106 in such a way as to be pressed against the surface of the fixing roller 106 by an elastic force of a torsion coil spring 117. A discharge guide 118 for guiding the recording paper 101 in a discharging direction is attached to a lower portion of the torsion coil spring 117. Moreover, paired upper and lower discharging rollers 119 for discharging the recording paper 101 to the outside of the fixing apparatus 103 are provided above and under the discharge guide 118, respectively.
Next, the detail structure of the pressure releasing mechanism of the conventional fixing apparatus is described hereinbelow by referring to FIGS. 16 to 20. As shown in FIGS. 16 to 20, this pressure releasing mechanism of the conventional fixing apparatus includes a crank-plate 112, an extension coil spring 115, a crankshaft 120, a cam 121, an electromagnetic valve 122, a cam/electromagnetic-valve mounting member 123, a shaft screw 124, a nut 125, and a screw 126.
As shown in FIGS. 16 and 17, end portions 120a and 120b formed by bending both tip end parts of the crankshaft 120 in directions almost orthogonal to each other are provided therein. Further, as shown in FIGS. 16 to 18, a cam 121 includes a cam shaft 121a, an electromagnetic valve abutting portion 121b, and an engaging portion 121c. Furthermore, as shown in FIG. 19, the electromagnetic valve 122 includes an E-ring 122a, a compression coil spring 122b, a nut 122c, a body portion 122d, and a rod portion 122e. This body portion 122d is provided with a nut mounting portion 122f, and a throughhole 122g, through which the rod portion 122e is passed. The rod portion 122e is provided with a groove 122h to which the E-ring 122a is fitted. Also, the rod portion 122e has a movable tip portion 122i provided at the top end thereof. Furthermore, as shown in FIGS. 16 and 20, a cam/electromagnetic-valve member 123 includes paired upper and lower axial screw holes 123a, an electromagnetic valve mounting hole 123b, and two leg portions 123c. 
Further, as shown in FIG. 16, one of the end portions 120a of the crankshaft 120 engages with the engaging hole 112c of the crank-plate 112. Further, the other end portion 120b of the crankshaft 120 engages with the engaging hole 121c of the cam 121. Additionally, the cam 121 is provided at the electromagnetic mounting member 123 by the axial screw 124, which is inserted into the paired upper and lower axial screw insertion holes 123a of the cam/electromagnetic-valve mounting member 123, in such a way as to be able to turn around the cam shaft 121a serving as a supporting point. Further, the electromagnetic valve 122 is attached to the cam/electromagnetic-valve member by inserting the nut mounting portion 122f of the electromagnetic valve 122 into the electromagnetic valve mounting hole 123b of the cam/electromagnetic valve mounting member 123 and then screwing the nut 122c thereon. Further, the movable tip portion 122i of the electromagnetic valve 122 abuts against the electromagnetic valve abutting portion 121b of the cam 121. Besides, in a state in which the pressure roller 109 is pressed against the fixing roller 106 by a pressing force of the extension coil spring 115, the movable tip portion of the electromagnetic valve 122 is in a retreated condition, as shown in FIG. 17. Furthermore, the cam/electromagnetic-valve mounting member 123 is fixed to a frame 104 by a screw 126, as shown in FIGS. 17 and 20.
Next, an operation of the conventional fixing apparatus 103 is described hereinbelow by referring to FIGS. 16 to 18. First, the recording paper 101, on which a toner image is transferred, is guided by the entrance guide 107, and inserted into between the fixing roller 106 and the pressure roller 109. The inserted recording paper 101 is heated by the fixing roller 106 having been heated to about 200. C. Also, the recording paper 101 is pressed by the pressure roller 109 against the surface of the fixing roller 106. Consequently, the toner image, which is transferred onto the recording paper 101, is fixed thereto. Then, the fixing roller 106 rotates in a conveying direction (clockwise) to thereby feed the recording paper 101, to which the toner image is fixed, to a discharging side. Subsequently, the recording paper 101 is separated from the surface of the fixing roller 106 by the separating claw 116 provided in such a manner as to touch the surface of the fixing roller 106.
Further, an operation of the pressure releasing mechanism of the conventional fixing apparatus 103 is performed as follows. First, when electric power is supplied to the electromagnetic valve 122 having been in a normal condition (see FIG. 17), the movable tip portion 122i of the electromagnetic valve 122 is driven in a direction of an arrow C in FIG. 17. Consequently, the electromagnetic valve abutting portion 121b is pressed by the movable tip portion 122i of the electromagnetic valve 122. Thus, the cam 121 turns around the cam shaft 121a serving as a supporting point (see FIG. 20) in a direction of an arrow D in FIG. 17. Then, the turn of the cam 121 in the direction of the arrow D in FIG. 17 causes the crankshaft 120, which connects the cam 121 to the crank-plate 112, to operate in such a way as to pull the crank-plate 112 horizontally (in a direction of an arrow E shown in FIG. 17). Consequently, as shown in FIG. 16, the crank-plate 112 turns around the shaft 114, which serves as a supporting point, against the force of the extension coil spring 115 in a direction (a direction of an arrow F in FIG. 16), so that the pressure applied to the fixing roller 106 by the pressure roller 109 is released. Thus, the apparatus is put into a condition shown in FIGS. 16 and 18. Consequently, the pressing force of the pressure roller 109 is released.
A third example of the conventional fixing apparatus shown in FIG. 16, which has an electromagnetic valve mounting portion, has a problem that the number of components is large because the pressure releasing mechanism includes nine components, that is, the crank-plate 112, the extension coil spring 115, the crankshaft 120, the cam 121, the electromagnetic valve 122, the cam/electromagnetic-valve the axial screw 124, the nut 125, and the screw 126.
Further, in the structure disclosed in the JP-UM-A-56-89215, the yoke (the electromagnetic valve mounting portion) for mounting the electromagnetic valve thereon is formed integrally with a chassis (a frame) by being cut upwardly from the chassis (the frame). However, in the case of using the electromagnetic valve (the solenoid), which is described in the JP-UM-A-56-89215, as a drive source for the pressure releasing mechanism of the conventional fixing apparatus shown in FIG. 15, this conventional apparatus has a disadvantage in that a cam mounting member for mounting the cam, which abuts against a movable iron core of the electromagnetic valve (the solenoid), should separately be provided therein. Consequently, even in the case of applying the structure, which is disclosed in the JP-UM-A-56-89215, to the conventional fixing apparatus, this conventional apparatus has the problem that the number of components thereof is large.
Furthermore, in the structure disclosed in the JP-UM-A-58-105106, two metal fittings and one frame element are needed for fixing the electromagnetic valve (the solenoid). Thus, this conventional apparatus has a disadvantage in that the number of components increases. Moreover, in the case of using the solenoid as a drive source for the pressure releasing mechanism of the conventional fixing apparatus shown in FIG. 15, screws or the like for mounting the frame element, to which the solenoid is fixed, on the frame of the fixing apparatus is additionally needed. In addition, the cam mounting member for mounting the cam, which abuts against a plunger of the electromagnetic valve, should separately be provided therein. Thus, this conventional fixing apparatus has the problem that the number of components thereof is large, similarly to the third example of the conventional fixing apparatus having the electromagnetic mounting portion.